1. Field of the Invention
The invention is directed to portable work lights and more particularly to potable work lights employing fluorescent tubes which can be suspended adjacent a work area.
2. Description of the Prior Art
The usual work lights found in the prior art consist of an incandescent bulb mounted in a socket surrounded by a cage constructed of metal wires welded, braised or otherwise joined or of a cage molded entirely of plastic or rubber. These cages are intended to protect the lamp bulb from damage by limiting access to them. The bulbs are also susceptible to damage due to shock when dropped or struck against or by some object. Certain specialized "rough service" bulbs are offered which are asserted to be less susceptible to shock damage. In use incandescent bulbs, provide a limited area of lighting and give off a great deal of heat requiring placement of the lap at some distance from the work area thereby decreasing the light available a such work area.
Fluorescent lamp bulbs have a number of distinct advantages over incandescent lamp bulbs of the same rated wattage. The fluorescent lamp bulbs give off more light, produce less heat and glare and will last for a longer period of time. Also, the fluorescent lamp will illuminate a larger area and because of its cool operation may be placed closer to the work area.
However, adapting the usual straight robe fluorescent lamp bulb for use as a work light has a created a number of problems associated with the rather flimsy end cap and contact pins mounted thereon located at each end of the tube. Available fluorescent lamp bulb sockets are not able to maintain, throughout the bulb's serviceable life, a good electrical connection with the bulb end pins. Even a good initial connection between the bulb pins and the bulb socket does not guarantee a continued good contact therebetween as the bulb/socket combinations are subjected to rough use in the field. Without good contact the fluorescent bulb may not light or if it does it will result in a dangerous high impedance joint.
In order to overcome the contact problems between the bulb pins and the sockets. the sockets have been made larger and stronger which makes them difficult to use on a portable light source where weight is a considerable factor.
Also, in order to protect the fluorescent bulb, a plastic tube is usually placed about such fluorescent bulb which introduces problems of thermal expansion of the plastic tube if one or both of the bulb sockets is mounted upon the plastic tube. The U.S. Pat. No. 4,092,706 to Vest discloses a fluorescent light designed to accommodate elongation of a plastic tube due to thermal expansion of such plastic tube upon which the tube sockets are mounted. A metal four-legged socket support with a flexible inner leg is employed to maintain electrical contact with the fluorescent tube despite changes in the length of such plastic tube.
A further problem exists with a portable fluorescent bulb device. That is, that electrical connections must be made to both ends of the fluorescent bulb. The fluorescent bulb could be placed mid-span of the electrical conductors powering the bulb or the bulb could be placed at the conductor ends with one or more conductors passing over or within the support plastic robe of the portable fluorescent bulb. In U.S. Pat. No. 4,088,882 to Lewis, he shows a fluorescent lamp unit for a bicycle in which the end caps are adhesively bonded to the ends of the fluorescent bulb to establish and maintain a good electrical connection between the bulb pins and the socket. In addition, one conductor extends between the bulb end caps as a helix over the face of the bulb itself where it is subject to damage or full or partial removal from the respective end caps.
U.S. Pat. No. 4,262,327 to Kovacik shows a portable fluorescent tube work light having an outer tubular envelope about the fluorescent tube with end sockets at both ends. Conductors 106, 107 extend from one end of the fluorescent tube to the other within the tubular envelope and adjacent to and most likely in direct contact with the fluorescent tube. Despite its lower generation of heat as compared to an incandescent lamp, the heat in a confined space may be sufficient to destroy the insulation on the two conductors and cause the fluorescent tube and its associated circuits to be shorted out or otherwise affected.